In the field of manufacturing integrated circuit elements, miniaturization of processing size in lithographic process is proceeding in order to achieve higher degrees of integration, and in recent years the development of technology enabling fine processing in the submicron order is advancing. In this lithographic process, a resist is applied onto a substrate, and then a mask pattern is transferred to the resist by exposure to radiation and developed with a suitable developer to form a desired resist pattern. However, many substrates used in the field of manufacturing integrated circuit elements have high reflectivity, and there is a problem of standing waves based on the interference between exposure light and reflected light off a substrate, and another problem is that particularly when a substrate having uneven surface is used as a substrate to be coated with a resist, an exposure light passing through the resist layer is reflected off the substrate whereby the light reaches the resist portion which should not be exposed to the light, thus causing pattern defects or resulting in a failure to obtain a pattern having desired resolution or desired shapes.
To solve these problems, various methods have been proposed so far. The known methods include e.g. a method of dispersing, in a resist, a dye having absorption in the wavelength range of exposure light, a method of forming an anti-reflective coating consisting of an inorganic compound coating such as titanium nitride etc. on a substrate by CVD or vacuum deposition, a method of forming an anti-reflective coating by applying onto a substrate an organic polymer solution having a radiation absorbing dye dispersed or dissolved therein, and a method of forming a radiation absorbing coating by applying onto a substrate a radiation absorbing polymer having a chromophore bound chemically to the polymer.
Among these methods, the method of dispersing a radiation absorbing dye in a resist has problems such as reduction in resist sensitivity, thinning of the resist layer during development and sublimation of the dye during baking. On the one hand, the method of using an inorganic anti-reflective coating has various problems such as difficulty in accurate control of coating thickness, difficulty of forming a coating with uniform thickness, requirement for a special apparatus upon conducting vacuum deposition, poor adhesion to a resist film, and necessity of another dry etching process in order to transfer a pattern. Further, the method of dispersing a radiation absorbing dye in an anti-reflective coating has problems such as separation of the dye from the polymer upon forming an anti-reflective coating by spin coating, elution of the dye into a resist solvent, and sublimation of the dye into a resist film at the time of baking. Furthermore, some anti-reflective coatings using the organic substance described above, particularly containing a low-molecular dye dispersed in the polymer, fail to form a coating with uniform thickness on a substrate with uneven surface.
On the other hand, the method of using a radiation-absorbing polymer having a chromophore bound chemically to the polymer does not have such drawbacks, so this method has attracted attention in recent years. The method of forming an anti-reflective coating by use of a radiation absorbing polymer, and the radiation absorbing polymer material used in this method, are described in e.g. JP-A 6-75378, JP-A 6-118656, WO 9412912, U.S. Pat. No. 4,910,122 and U.S. Pat. No. 5,057,399. In production of LSI in recent years, deep ultraviolet rays (DUV) with a wavelength of 248 nm or less comes to be used for exposure of a photoresist to achieve high resolution, and in particular when a certain radiation of such short wavelength is used for exposure, an anti-reflective coating is essential to keep the good resolution and good pattern shape of a resist image to be formed. As the anti-reflective coating materials for i-line using a radiation absorbing polymer, anti-reflective coating materials, e.g. AZ.RTM.-BARLi.RTM. (Clariant Co.), which can form an anti-reflective coating with uniform thickness even on a substrate with uneven surface, that is, which is excellent in step coverage and other characteristics are known. But under the present circumstances, there is no anti-reflective coating material for DUV, which particularly has step coverage similar to or more than that of AZ.RTM.-BARLi.RTM. and is excellent in other properties such as radiation absorption characteristics, etching characteristics and adhesion to a substrate.
The object of the present invention is to provide an anti-reflective coating free of the problems in the prior art described above, that is, a coating which is excellent in step coverage, does not cause transfer and sublimation of a dye during heating, has a high anti-reflectivity effect, is also excellent in adhesion to a substrate, dry etching properties, thermostability and handling, and is capable of forming a high-resolution resist image excellent in pattern shape; a novel radiation absorbing polymer having a radiation absorbing dye bound chemically to a polymer chain thereof, which is used in said coating; a method of preparing the same; and a film forming composition containing said novel radiation absorbing polymer.